1. Field of the Invention
The present invention relates to a multi-layer label film that comprises layers that are connected with one another.
2. The Prior Art
At present, label films are predominantly produced from medium-density polyethylene (MDPE), i.e. with a density of 0.930-0.935 g/cm3. These films are usually offered on the market starting from a minimum thickness of 95 xcexcm. The films are characterized by good rigidity and very good behavior during punching. Further reductions in thickness, in the case of this raw material, result in drastic losses in rigidity, which is important for the ability to dispense the labels at the processing facility. For this reason, high-density polyethylene (HDPE), with a density of 0.955-0.965 g/cm3, is used for films that are thinner than 90 xcexcm, in order to balance out the loss in rigidity. The disadvantage of these label films, which can contain 20-50 wt.-% HDPE, depending on the thickness, is that with an increasing HDPE content, the behavior during punching clearly deteriorates. Both film types are usually produced as single-layer or symmetrically structured multi-layer films, in order to counteract a tendency of the label to roll up.
A multi-layer fabric material is known from EP-B-0335 425, which comprises layers connected with one another. This is a co-extrudate made of a relatively thick core layer made of a polymer film material and a relatively thin surface layer made of polymer film material on the top of the co-extrudate. The material has a surface that can be printed on with printing ink, and a layer of a pressure-sensitive adhesive that is arranged on the side of the extrudate that faces away from the top. The material is used for the production of labels. In this known material, the core layer consists of low-density, medium-density, or high-density polyethylene, while the thin surface layer can consist of ethylene vinyl acetate, polyvinyl chloride, or other polymers, with the exception of polyethylene. In each case, the core layer and the thin surface layer are therefore produced from different materials. This results in a material mix, which is a disadvantage with regard to production, and particularly with regard to disposal of the material.
It is an object of the present invention to provide a label film that avoids the disadvantages of the prior art as described. The label film according to the invention has the advantages that it has no tendency to roll up, and is easy to punch.
The above objects are accomplished with a multi-layer label film of the type stated initially that has the layer sequence as follows. In this connection, LDPE=low-density polyethylene is defined as follows: low-density PE; density between 0.928 and 0.935 g/cm3.
A printable first layer that has a thickness of 60-80 xcexcm and consists of 60-80 wt.-% LDPE and 40-20 wt.-% HDPE, a second layer that has a thickness of 10-20 xcexcm and consists of 100 wt.-% LDPE, and an adhesive layer that is arranged on the HDPE-free side of the second layer, as well as a carrier material. The HDPE-free side of the second layer is that side not in contact with the first layer. The printable first layer and the second layer are formed by co-extrusion.
It is advantageous if the first layer of the label film is in turn made up of at least two layers; in the case of two layers, the layer arranged on the outside can have a thickness of 10-30 xcexcm and consist of 70-90 wt.-% LDPE and 10-30 wt.-% HDPE, and the additional layer can have a thickness of 40-50 xcexcm and consist of 50-69 wt.-% LDPE and 31-50 wt.-% HDPE.
This film is therefore characterized in that an outside layer is produced from conventional LDPE. This layer represents the back of the finished label, which is coated with a pressure-sensitive adhesive. The other two layers contain HDPE. During rotation punching or flat-bed punching of the finished label laminate, which consists of the label coated with adhesive and here is laminated against silicone paper as the release, the punching resistance is clearly reduced by the HDPE-free LDPE layer that lies towards the silicone paper. During punching, only the label is to be punched through, not the silicone paper.
Therefore the blades of the punching die are adjusted in such a way that they just punch through the label, but only make a slight partial punch in the paper, without damaging it. The greatest punching force is applied when breaking through the surface of the label, which contains LDPE. The less strong LDPE layer reduces the punching force when the punching blades exit from it. In practical situations, it sometimes occurs that the labels are not completely punched out. Because the LDPE layer is less strong, the labels can nevertheless be more easily processed, because the LDPE tears more easily, because of its lower tear propagation resistance, than the LDPE layer that contains HDPE.
It is preferable if the LDPE used for production of the labels has a density of 0.928-0.935 g/cm3, and if the HDPE has a density of 0.955-0.965 g/cm3.
It is preferable if the layer thickness ratio of the layers is (11):(12):(2)=1-4:2-5:1.
In a particularly preferred embodiment of the label film according to the invention, the layer thickness ratio is (11):(12):(2)=1.7:3:1.
It is advantageous if silicone coated paper is used as the carrier material. Other release films are also possible, such as those with polyolefins as the carrier film, for example polybutylene or polypropylene as the polyolefin.